1. Field of the Invention
This invention relates to a mechanical mounting for a zoom lens, and more particularly to a mounting for a zoom lens capable of closeup photoraphy beyond the usual focusing range.
In FIGS. 1a and 1b, lens I represents a focusing lens movable along an optical axis 01-02 by rotative operation of a focusing actuator about the optical axis, and lenses II and III represent a zooming lens system movable along the optical axis 01-02 to effect variation of image magnification and image shift compensation by rotative or linear operation of a zooming actuator about or along the optical axis 01-02. Dashed lines, x and y, indicate traces of movement of the variator II and compensator III.
FIG. 1a illustrates the various lens components with the zooming actuator set in the telephoto position in which the focusing lens component I is rendered movable towards an object to be photographed until closeup photography from a distance, for example, 0.8 meters becomes possible. When in the wide angle position of FIG. 1c, the focusing lens component I can be closed to 1.0 meter, whereby the image angle of the focusing component I is widened from .epsilon..sub.1 through .epsilon..sub.2 to .epsilon..sub.3 as the focal length of the entire system changes from the longest through the middle to the shortest focal length, as illustrated in FIG. 1.
Therefore, in order to accomplish closeup photography by axially moving the focusing component beyond the usual focusing component and beyond the usual focusing range towards closer object distances without introducing some vignetting, total movement of the lens components II and III contributing to the zooming action must be limited to a shortened range.
2. Description of the Prior Art
Prior art in the field of the invention includes U.S. Pat. No. 4,210,387.
In U.S. Pat. No. 4,210,387, focusing beyond the usual range of object distances towards shorter ones in particular focal length settings, the mounting mechanism is characterized by the following feature:
A stopper member is either in fixedly secured relation to, or in differential relation to, the zooming control member to define the forward range movement limit of the focusing control member.
In the zoom lens mounting mechanism of this construction, the following phenomenon takes place. Referring to FIG. 1d, there is shown a graph where the abscissa is in the position of the zoom control member with variation of the focal length of the entire system. The ordinate is in the position of the focusing control member with variation of the object distance, and where a point, a, indicates the closest object distance possible beyond the usual focusing range when in the telephoto setting, and another point, b, indicates the shortest focusable object distance when in the wide angle setting, being shiftable depending upon the focal length position.
The mounting mechanism of U.S. Pat. No. 4,210,387 operates in such a manner that, assuming that the variator sleeve member 5 is first set at the aforesaid point, a, then when it moves towards the wide angle side to change the focal length, the focusing member 1 follows up through the stopper 10, while the closest possible object distance is changed along a curved line, c, in FIG. 1d.
Alternatively assuming that the variator sleeve member 5 lines upon the aforesaid point, b, then when the focusing member 1 moves to effect focusing from a shorter object distance to the closest, the variator sleeve member 5 changes the focal length along a curved line, d, in FIG. 1d.
In conclusion, the mounting mechanism of U.S. Pat. No. 4,210,387 has the disadvantage that the focusing member is shifted, during zooming or that the variator sleeve member is shifted during focusing.
An object of the present invention is to provide a mechanical mounting for a zoom lens with a focusing actuator movable beyond the usual focusing range to closer object distances to effect closeup shooting, wherein when the focusing actuator is in the closeup range, the range of movement of the zooming control member is readjusted depending upon the position of the focusing actuator, whereby the maximum possible image angle can be adjusted in accordance with the object distance.
Another object of the present invention is to provide a mechanical mounting which has solved the above-described problem without making the structure complicated and minimizing the number of constituent parts.